U.S. patent number 5,013,126 [Application Number 07/594,544] was granted by the patent office on 1991-05-07 for waterproof optical fiber cable.
This patent grant is currently assigned to Sumitomo Electric Industries Ltd.. Invention is credited to Nobuhiro Akasaka, Tomoyuki Hattori, Toru Yamanishi.
United States Patent |
5,013,126 |
Hattori , et al. |
May 7, 1991 |
Waterproof optical fiber cable
Abstract
A waterproof optical fiber cable comprising at least one coated
optical fiber and a waterproof compound surround said at least one
coated optical fiber, wherein a swelling degree of a coating
material of the optical fiber induced by said waterproof compound
is not larger than 10%, which optical fiber cable has stable
performances.
Inventors: |
Hattori; Tomoyuki (Yokohama,
JP), Akasaka; Nobuhiro (Yokohama, JP),
Yamanishi; Toru (Yokohama, JP) |
Assignee: |
Sumitomo Electric Industries
Ltd. (Osaka, JP)
|
Family
ID: |
26545377 |
Appl.
No.: |
07/594,544 |
Filed: |
October 9, 1990 |
Foreign Application Priority Data
|
|
|
|
|
Oct 9, 1989 [JP] |
|
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1-262096 |
Oct 9, 1989 [JP] |
|
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1-263583 |
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Current U.S.
Class: |
385/103;
523/173 |
Current CPC
Class: |
G02B
6/4494 (20130101); G02B 6/4408 (20130101); H01B
7/282 (20130101); H01B 7/285 (20130101) |
Current International
Class: |
G02B
6/44 (20060101); H01B 7/17 (20060101); H01B
7/282 (20060101); H01B 7/285 (20060101); G02B
006/44 (); H02G 015/00 () |
Field of
Search: |
;350/96.10,96.23,96.33,96.34 ;174/7R,11SR,22R,23R,23C ;252/582,583
;523/173 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Healy; Brian
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. A waterproof optical fiber cable which comprises at least one
coated optical fiber and a waterproof compound surrounding said at
least one coated optical fiber, wherein a swelling degree of a
coating material of the optical fiber induced by said waterproof
compound is not larger than 10%.
2. The waterproof optical fiber cable according to claim 1, wherein
said waterproof compound comprises an oil component, a thickening
agent and an agent for preventing oil separation.
3. The waterproof optical fiber cable according to claim 2, wherein
said waterproof compound contains no oil component having a
molecular weight of smaller than 300.
4. The waterproof optical fiber cable according to claim 1, wherein
said waterproof compound has a cone penetration of at least 200 at
-40.degree. C. and not larger than 450 at 80.degree. C.
5. The waterproof optical fiber cable according to claim 4, wherein
said waterproof compound comprises an oil component having a pour
point of not higher than -30.degree. C.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water proof optical fiber cable
for optical communication.
2. Description of the Related Art
A waterproof communication cable which comprises stranded element
wires each comprising a copper conductor coated with a plastic
coating such as polyethylene- and polypropylene, a waterproof
compound filled in spaces in the cable and an outer sheath is used
as a maintenance-free communication cable. As the waterproof
compound, a compound comprising a polybutene base oil and low
molecular weight polyethylene, a compound comprising a petrolatum
base oil and low molecular weight polyethylene and the like are
known. As disclosed, for example, in Japanese Patent Kokai
Publication No. 202015/1982, the waterproof compound is heated and
molten and poured in the spaces in the cable. since the
conventional waterproof compound is filled in the cable space in
the molten state, in case of an optical fiber cable, volume
shrinkage of the waterproof compound during cooling generates short
period small bending, namely microbending on each optical fiber and
increases light transmission loss.
As a waterproof compound for an optical fiber cable Japanese Patent
Kokai Publication No. 126706/1986 discloses a waterproof compound
for an optical fiber cable comprising a synthetic oil and
optionally a mineral oil, and Japanese Patent Kokai Publication No.
8777/1983 discloses a waterproof compound for an optical fiber
cable comprising a mineral oil and hydrophobic silica.
In addition to the already described problem encountered in the
production of the waterproof optical fiber cable, the conventional
waterproof optical fiber cables have following three problems:
(A) Increase of transmission loss at low temperatures.
(B) Deterioration of a coating material of the optical fiber,
(C) Bleeding of the waterproof compound from cable ends.
A cause for the problem (A), namely the increase of transmission
loss at low temperature is that the waterproof compound solidifies
and shrinks at low temperature and tightens the optical fiber to
generate the microbending on the optical fiber.
A cause for the problem (B), namely the deterioration of the
coating material of the optical fiber, is that an oil component
which is the main component of the waterproof compound tends to
penetrate in the coating material of the optical fiber and swells
or deteriorates the coating material, since the oil component is a
hydrocarbon base oil. For example, it is known from Japanese Patent
Kokai No. 100036/1988 that an oil in the waterproof compound
penetrates in the coating material of the optical fiber to generate
stress therein, whereby the microbending is generated on the
optical fiber. To solve such problem, it is proposed to reduce
influence of the oil to the coating material by decreasing amounts
of aromatic components in the oil and polarity of the oil as much
as possible (see, for example, Japanese Patent Kokai Publication
No. 213813/1986). Since water absorbance of the coating material of
the optical fiber is made low recently and polarity of the coating
material is made smaller than ever, it is difficult to prevent
swelling of the coating material by suppressing the polarity of the
oil component.
The bleeding of the waterproof compound from the cable ends (C)
means flowing out of the waterproof compound as such or the oil
component in the waterproof compound from the cable ends and
decreases workability or makes it impossible to connect the optical
fibers.
Hitherto, no waterproof compound can solve all the above problems
(A), (B) and (C).
SUMMARY OF THE INVENTION
An object of the present invention is to provide a waterproof
optical fiber cable which does not suffer from increase of
transmission loss at low temperature.
Another object of the present invention is to provide a waterproof
optical fiber cable in which a coating material of the optical
fiber is not deteriorated.
A further object of the present invention is to provide a
waterproof optical fiber cable from which a waterproof compound
does not bleed out.
According to the present invention, there is provided a waterproof
optical fiber cable which comprises at least one coated optical
fiber and a waterproof compound surrounding said at least one
coated optical fiber wherein a swelling degree of a coating
material of the optical fiber induced by said waterproof compound
is not larger than 10%.
The waterproof compound preferably contains no oil component having
a molecular weight of smaller than 300. In addition, the waterproof
compound preferably has a cone penetration value of at least 200 at
-40.degree. C and not larger than 450 at 80.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B show cross sections of coated optical fibers,
and
FIGS. 2, 3 and 4 show cross sections of preferred embodiments of
the waterproof optical fiber cable according to the present
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B show cross sections of optical fibers. The single
optical fiber 1 of FIG. 1A comprises a bare optical fiber 11 for
light transmission and two coating layers 12 and 13. The bare
optical fiber 11 may be made of quartz glass, and the coating layer
13 may be neglected. The multiple optical fiber 10 of FIG. 1B
comprises plural single optical fibers 1 and an outer coating layer
14 which bundles the optical fibers 1. The optical fiber 10 may be
called as a coated optical fiber tape.
The coating layers 12, 13 and 14 of the optical fibers 1 and 10
protect the bare optical fiber 11 from damage and impart
flexibility to the fibers. Examples of a coating layer material are
urethane-acrylate base resin, epoxy-acrylate resin,
silicone-acrylate resin, fluoride-acrylate resin and the like.
The waterproof compound comprises an oil component (e.g. silicone
oil, polybutene oil, .alpha.-olefin oil, mineral oil, etc.), a
thickening agent (e.g. silica, bentonite, clay, etc.) and an agent
for preventing oil separation (e.g. styrene base block copolymers,
etc.). The waterproof compound may further comprise other
conventional additives such as an antioxidant and an ultraviolet
light stabilizer.
To decrease the swelling degree of the coating material with the
waterproof compound to 10% or less, a molecular weight of the oil
component is suitably selected as seen from Examples below.
The swelling degree is expressed by a percentage of a weight of a
solvent (oil component) absorbed by a material based on an initial
weight of the material.
With the conventional waterproof compound, the oil component
penetrates in the coating material of the optical fiber. Thereby,
the stress is generated in the coating layer so that the
transmission loss is increased as explained above. In addition,
when the oil component reaches an interface between the optical
fiber glass and the coating layer, a force required for pulling out
the optical fiber glass from the coating material is decreased,
this resulting in difficulty in connection of the optical fibers.
The above problems are mainly caused by the swelling of the coating
material of the optical fiber due to penetration of the oil
component in the waterproof compound. However, when the swelling
degree of the coating material of the optical fiber induced by the
waterproof compound is not larger than 10%, the optical fiber cable
has stable properties.
A manner for suppressing the swelling degree to 10% or less is
explained. When a crosslink density in the coating material is
increased, swelling of the coating material can be prevented.
However, the increase of crosslink density leads to decrease of
elongation and increase of cure shrinkage. Therefore, the coating
material having the increased crosslink density is unsuitable. In
the course of the study, it has been found that the oil component
having a molecular weight of smaller than 300 penetrates in the
coating material of the optical fiber. Then, the use of an oil
component containing no component having the molecular weight of
smaller than 300, in particular a synthetic oil such as
.alpha.-olefin oil, or a mineral oil from which such low molecular
component is removed can provide the stable waterproof optical
fiber cable.
In a preferred embodiment, the waterproof compound has a cone
penetration value of at least 200 at -40.degree. C. and not larger
than 450 at 80.degree. C. When the cone penetration value is
smaller than 200 at -40.degree. C., the transmission loss increases
at low temperature. When the cone penetration value exceeds 450 at
80.degree. C., drip occurs at high temperature.
The waterproof compound having the above range cone penetration can
be prepared by selecting the oil component and the thickening agent
and also a ratio of these two components.
The cone penetration is a criteria of hardness of the waterproof
compound which is determined according to JIS K 2220. The smaller
cone penetration value means larger hardness.
To obtain the waterproof compound having such cone penetration, an
oil having a pour point of -30.degree. C. or lower, or an oil
having an average molecular weight of 3000 or smaller is preferably
used.
PREFERRED EMBODIMENTS OF THE INVENTION
Now, the preferred embodiments of the waterproof optical fiber
cable of the present invention will be explained.
FIG. 2 is a cross section of a first embodiment of the waterproof
optical fiber cable of the present invention.
Six coated optical fibers as shown in FIG. 1A are contained in an
polyamide tube 3 having an inner diameter of 1.4 mm and an outer
diameter of 2.0 mm to form a so-called loose tubes. In the tube 3,
the waterproof compound 2 of the present invention is filled.
The coated optical fiber 1 comprises a single mode optical fiber
having a diameter of 125 .mu.m and two coating layers made of a UV
curable resin having an outer diameter of 250 .mu.m.
Plural loose tubes, for example, six loose tubes as shown in FIG. 2
are stranded around a tension member 4 having a plastic coating 4a
at a suitable pitch. In gaps between pitches, the conventional
polybutene base waterproof compound 6 is filled. Around the
stranded loose tubes, an outer coating layer 5 is formed by
extrusion to produce a waterproof optical fiber cable.
Seven waterproof optical fiber cables were produced by changing the
kinds of the waterproof compounds filled in the polyamide tube 3.
The molecular weight distribution, the cone penetration and the
swelling degree of the coating material at room temperature are
shown in Table 1. The sample Nos. A and D used the waterproof
compounds according to the present invention, while the sample Nos.
E, F and G were comparative. "X" and "Y" stand for the resins used
in the first and second coating layers, respectively and both are
urethane-acrylate resins.
TABLE 1
__________________________________________________________________________
Sample No. A B C D E F G
__________________________________________________________________________
Composition*.sup.1 (wt. %) .alpha.-Olefin oil 74 86 88 92
Polybutene oil 92 Mineral oil 83 Silicone oil 87 Colloidal silica
10 7 8 10 3 7 3 Styrene base copolymer 15 6 4 6 4 4 4 Antioxidant 1
1 1 1 1 1 1 Molecular weight 350- 350- 900- 400- 200- 200- 200-
distribution 3500 3500 10000 4000 2500 3000 3000 Cone penetration
at 80.degree. C. 378 343 340 399 463 299 470 50.degree. C. 375 341
300 392 440 271 448 25.degree. C. 360 338 283 377 392 255 395
0.degree. C. 351 318 274 350 384 236 365 -20.degree. C. 336 303 249
339 309 203 347 -40.degree. C. 315 283 239 242 197 187 309 Swelling
degree (wt. %) Resin X 7.3 4.9 3.5 6.1 12.4 10.5 10.5 Resin Y 3.2
2.0 1.4 2.4 9.6 8.4 8.4
__________________________________________________________________________
Note:*.sup.1 Olefin oil: Polybutene oil: Mineral oil: Silicone oil:
Styrene base copolymer: Antioxidant:
The original transmission loss at -40.degree. C. with light having
a wavelength of 1.55 .mu.m and the results of the drip test are
shown in Table 2.
The drip test was conducted according to Bellcore Specification
TR-TSY-000020 at 65.degree. C.
With each of the produced waterproof optical cables, after six
months, change of the transmission loss and change of the force
required for pulling out the optical fibers from the polyamide
imide tube were evaluated. The results are shown in Table 2.
TABLE 2
__________________________________________________________________________
Sample No. A B C D E F G
__________________________________________________________________________
Transmission +0.02 +0.03 +0.02 +0.03 +0.13 +0.21 +0.02 loss at
-40.degree. C. (dB/km)*.sup.1 Drip test*.sup.2 O O O O X O X Change
of -16 +5 +10 -14 -65 -50 -55 force required for pulling out
optical fiber (%) Change of No No No No Yes Yes Yes transmission
loss after six months
__________________________________________________________________________
Note: *.sup.1 An average value of six coated optical fibers in
comparison with transmission loss at 25.degree. C. *.sup.2 O: Pass,
X: Fail.
The above results confirmed that the waterproof compounds according
to the present invention are suitable for waterproofing the optical
fiber cable, since the transmission loss at -40.degree. C. does not
increase significantly and the compound does not bleed out from the
cable end.
FIG. 3 shows a cross section of a second embodiment of the
waterproof optical fiber cable of the present invention. In this
embodiment, the plural coated optical fibers 1 are contained in
each groove 7a formed on a perifibers phery of a spacer 7 which has
a tension member 4 at its center. Each groove 7a is filled with the
waterproof compound 2 of the present invention. Around the spacer
7, a wrapping tape 8 is wound. Further, around the wrapped tape 8,
an outer coating layer 5 is provided.
FIG. 4 shows a cross section of a third embodiment of the
waterproof optical fiber cable of the present invention, which is
substantially the same as that of FIG. 3 except that the coated
optical fibers 10 of FIG. 1B are contained in each groove 7a.
* * * * *